In 3GPP LTE Release 11 system, one feature is an enhanced physical downlink control channel (EPDCCH). Compared to the legacy physical downlink control channel (PDCCH), the main motivation of the EPDCCH is                able to support increased control channel capacity;        able to support frequency-domain inter-cell interference coordination (ICIC);        able to achieve improved spatial reuse of a control channel resource;        able to support beamforming and/or diversity;        able to operate on the new carrier type (NCT) and in MBSFN subframes;        able to coexist on the same carrier as legacy user equipment (UE).        
In Release 11, the main design for the EPDCCH focuses on configuring an enhanced UE-specific search space (EUSS) in the EPDCCH detected by the UEs. Except for the predefined rules and parameters, all necessary configurations are from radio resource control (RRC) or higher layers. Further, the EPDCCH may not work without legacy PDCCH because no common search space is defined for the EPDCCH.
Up to now, the question of how to support the EPDCCH in a stand-alone operation, especially in cases with a stand-alone new carrier type (NCT), is still an open issue. In Release 12, the related topic in the 2nd level of the NCT is how to let the NCT operate independently without always being associated with a legacy carrier. In such a case, there is no legacy PDCCH, and all control signaling are assumed to be transmitted in the EPDCCH. Then, a stand-alone EPDCCH must be designed. In other words, an enhanced common search space (ECSS) should be supported in the EPDCCH by default and without the RRC or higher layers signaling to schedule the common control message.